Recent research in the field of nanometre-scale electronics has focused on two fundamental issues: the operating principles of small-scale devices, and schemes that lead to their realization and eventual integration into useful circuits. Experimental studies on molecular1 to submicrometre2 quantum dots and on the electrical transport in carbon nanotubes3,4,5 have confirmed theoretical predictions6,7,8 of an increasing role for charging effects as the device size diminishes. Nevertheless, the construction of nanometre-scale circuits from such devices remains problematic, largely owing to the difficulties of achieving inter-element wiring and electrical interfacing to macroscopic electrodes. The use of molecular recognition processes and the self-assembly of molecules into supramolecular structures9,10 might help overcome these difficulties. In this context, DNA has the appropriate molecular-recognition11 and mechanical12,13,14,15,16 properties, but poor electrical characteristics prevent its direct use in electrical circuits. Here we describe a two-step procedure that may allow the application of DNA to the construction of functional circuits. In our scheme, hybridization of the DNA molecule with surface-bound oligonucleotides is first used to stretch it between two gold electrodes; the DNA molecule is then used as a template for the vectorial growth of a 12 µm long, 100 nm wide conductive silver wire. The experiment confirms that the recognition capabilities of DNA can be exploited for the targeted attachment of functional wires.

DNA-templated assembly and electrode attachment of a conducting silver wire

This paper describes a novel fabrication method for the manufacture of three-dimensional (3D) interconnected microchannels. The fabrication is based on a full wafer polymer bonding process, using SU-8 polymer epoxy photoresist as a structural material. The technology development includes an improvement of the SU-8 photolithography process in order to produce high uniformity films with good adhesive properties. Hence, 3D embedded microchannels are fabricated by a low temperature adhesive bonding of the SU-8 photopatterned thick films. The bonding occurs at temperatures (100–120 °C) lower than those usually applied in bonding technology. The bonding process parameters have been chosen in order to achieve a strong and void-free bond. High bond strengths, up to 8 MPa, have been obtained. Several examples using this new technology are shown, including bonding between different combinations of silicon and Pyrex wafers. This method also allows us to bond wafers with previously surface micromachined structures. Interconnected microchannels with vertical smooth walls and aspect ratios up to five have been obtained. Channels from 40 to 60 µm depth and from 10 to 250 µm width have been achieved. Liquid has been introduced at different levels into the microchannels, verifying good sealing of the 3D interconnected microchannels. The fabrication procedure described in this paper is fast, reproducible, CMOS compatible and easily implementable using standard photolithography and bonding equipment.

https://iopscience.iop.org/article/10.1088/0960-1317/14/7/027/pdf

Novel three-dimensional embedded SU-8 microchannels fabricated using a low temperature full wafer adhesive bonding

Organic-inorganic hybrid films were prepared through layer-by-layer (LBL) deposition of poly(allylamine hydrochloride) (PAH) and ZrO(2) nanoparticles coated with poly(acrylic acid) (PAA), allowing facile control of surface roughness and hydrophobicity. Superhydrophobic behavior was observed after deposition of silica nanoparticles and a simple fluorination of the surface. The structure of films was controlled by the number of deposition cycles using PAA-coated 100 nm ZrO(2) nanoparticles, the particle size, and the prelayer with PAH and PAA. The change in the apparent water contact angle of (PAH/PAA-coated ZrO(2)n surfaces without fluorination of the surface agrees with Cassie and Baxter's model for nonwetted surfaces even though the outermost surface itself is hydrophilic. Superhydrophobic surfaces were then successfully developed by the deposition of hydrophilic silica nanoparticles on a 10 bilayer surface of PAH/PAA-coated ZrO(2), and a simple fluorination. Moreover, the chemical stability of the film was greatly increased by heat-induced cross-linking of the film. The incorporation of ZrO(2) nanoparticles in superhydrophobic films promises better mechanical properties than the organic film.

Stable superhydrophobic organic-inorganic hybrid films by electrostatic self-assembly.

We propose a new method for focus tracking during the recording of a sequence of digital holograms while the sample experiences axial displacement. Corrected reconstruction distances can be automatically calculated, and well-focused amplitude and phase-contrast images can be obtained for each digitized hologram. The method is demonstrated for inspection of microelectromechanical systems subjected to thermal load. The method can be applied as a quasi-real-time procedure.

Digital holographic microscope with automatic focus tracking by detecting sample displacement in real time

Transparent, Conductive, and Superhydrophobic Films from Stabilized Carbon Nanotube/Silane Sol Mixture Solution†

This paper presents a detailed study of the waveguide and plasmon polariton properties of four-layer systems involving highly doped semiconductor material. The dispersion relations of waveguide and plasmon polariton modes are calculated for different geometrical parameters and material properties. Special attention is paid to the transition region between the latter modes, which exhibits a complex behavior. Slab plasmon polaritons at wavelengths slightly larger than the plasma wavelength, yielding a positive real part of the permittivity, have been found. Finally, applications at wavelengths near the transition region and near the plasma wavelength are proposed and discussed.

Slab plasmon polaritons and waveguide modes in four-layer resonant semiconductor waveguides

A theoretical study of the reflection of a bounded Gaussian ultrasonic beam, incident onto a rectangular inclusion located near a fluid/solid half-space interface, is presented. The thickness of the inclusion is assumed to be much smaller than the ultrasonic wavelength in the solid. It is shown that, at critical Rayleigh angle incidence, the phase in the point of maximum amplitude of the shifted reflected lobe is very sensitive to dimension variations of the inclusion, and thus useful for inclusion characterization. The modelization of the problem is based on mode theory.

Bounded beam interaction with thin inclusions. Characterization by phase differences at Rayleigh angle incidence.

Nonlinear and bistable reflection minima in an ATR-configuration with a highly doped n-GaAs film at 10.6 micron

We performed a theoretical study about the optical nonlinearity connected with the redistribution of free electrons between the Γ and L valley of highly doped n-GaAs. An extended comparison was made between the intravalley (or nonparabolicity) and the intervalley contribution. In the energy relaxation process, intravalley transitions in the Γ and L valley by means of the emission of optical phonons and equivalent intervalley transitions in the L valley by means of intervalley phonons were considered as the main mechanism of energy transfer to the lattice. It is demonstrated that when the frequency of light matches with the plasma frequency of the n-doped GaAs the nonlinearity is quite big. At a doping concentration of 7×1018 cm−3 we calculated a nonlinear refractive index n2=1.74×10−8 cm2/W at 10.6 μm. The doping and intensity dependent energy relaxation times of electrons are calculated: for Γ-valley electrons τenΓ∼(3–5) ps and for L-valley electrons τenΓ∼(0.3–0.5) ps. It is believed that the response ti...

Comparative study of the intra- and intervalley contributions to the free-carrier induced optical nonlinearity in n-GaAs

A quantum mechanical model based on the second order perturbation theory was constructed for the calculation of the free-electron absorption coefficient in nonparabolic III–V semiconductors. The implemented model allows for the calculation of the absorption changes when the free-electron gas temperature differs from the lattice temperature. Several mechanisms, which assist in the photon absorption process, were taken into account. At the considered lattice and electron temperature range and doping concentrations, the most important scattering mechanisms are impurity scattering, thermal and hot longitudinal optical phonon scattering, and finally acoustic phonon scattering. For all the interaction potentials we included the effect of screening by the conduction electrons. The model was developed in a fully consistent nonparabolic way. The electron dispersion relation as well as the interaction probabilities feature nonparabolic effects. Computations are performed for GaAs, InAs, and InSb at different mid-IR...

Gennady Shkerdin

Papers

Slab plasmon polaritons and waveguide modes in four-layer resonant semiconductor waveguides

Bounded beam interaction with thin inclusions. Characterization by phase differences at Rayleigh angle incidence.

Nonlinear and bistable reflection minima in an ATR-configuration with a highly doped n-GaAs film at 10.6 micron

Comparative study of the intra- and intervalley contributions to the free-carrier induced optical nonlinearity in n-GaAs

Hot free-electron absorption in nonparabolic III–V semiconductors at mid-infrared wavelengths